For safety reasons, it is important to determine insulation resistances with respect to high-voltage devices.
WIPO Patent Application No. 2011/160881 A1 describes a method for determining the insulation resistance of an ungrounded electrical network, in which a measuring voltage may be fed into the network via a voltage divider. A measuring current flowing after applying the measuring voltage is measured during at least three different time intervals during a transient period of the network. The insulation resistance may be determined based on the measurement results. However, the method requires a high component complexity and includes a variety of drawbacks. For example, it is only possible to determine the overall insulation resistance, and partial insulation resistances cannot be determined.
German Patent Application No. 196 18 897 B4 describes a circuit for determining the insulation resistance of a battery (such as a rechargeable battery) in stand-alone operation. The circuit may determine the insulation resistance by measuring an open-circuit voltage and a load voltage, wherein a series connection of two capacitors may be connected to the battery terminals for storing the voltage values during the measurement, and the shared point of the capacitors may connect to a bleeder resistor. However, this requires long measuring times for large insulation capacitances.